Sigma
166715
225265378
2008-07-12T19:51:29Z
67.100.140.210
correct punctuation and capitalization
{{otheruses}}
{{wiktionarypar3|Σ|σ|ς}}
{{Table Greekletters|letter=sigma}}
[[Image:Madaba Jerusalem Mosaic.jpg|thumb|200px|The [[Madaba Map]], a sixth-century mosaic map of [[Jerusalem]] ("ΗΑΓΙΑ ПОΛΙΣ") uses the lunate sigma.]]
'''Sigma''' (upper case '''Σ''', lower case '''σ''', lower case in word-final position '''ς''') is the eighteenth letter of the [[Greek alphabet]]. In the system of [[Greek numerals]] it has a value of 200. When used at the end of a word, and the word is not all [[upper case]], the final form (ς) is used. (e.g. ''Ὀδυσσεύς'' (Odysseus) - Note the two sigmas in the center of the name, and the
word-final sigma at the end.) Not to be confused with the [[cedilla]] [[ç]].
The letter is ultimately derived from [[Phoenician alphabet|Phoenician]] [[Shin (letter)|Šin]] 𐤔. However, its name derives from [[Samekh]].
The uppercase form of sigma was borrowed into the [[Latin alphabet]] to serve as the uppercase of [[esh (letter)|esh]] (lowercase: {{unicode|ʃ}}).
== Lunate sigma ==
In Eastern forms of Greek writing (as opposed to the [[Western Greek alphabet]] used in the European Greek colonies) and in the Middle Ages, the '''lunate sigma''' (upper case {{Unicode|Ϲ}}, lower case {{Unicode|ϲ}}) — which resembles, but which is not at all related to, the [[Latin alphabet|Latin letter]] [[C]] — was often used. Lunate sigma was frequently used for writing [[Medieval Greek]], and it can still sometimes be seen in inscriptions in [[Eastern Orthodox Church|Greek Orthodox churches]], but also in certain printed editions of classical authors. The form of the [[Cyrillic alphabet|Cyrillic letter]] [[Es (Cyrillic)|С]] [s] and [[Coptic alphabet|Coptic letter]] ''sima'' are derived from lunate sigma.
On coins from the [[Indo-Greek|Hellenistic period in India]], the script of later coins sometimes use lunate sigma. This sigma continued to be written this way also in [[Medieval Greek]].
A dotted lunate sigma (''sigma periestigmenon'', encoded at U+03FE {{unicode|Ͼ}}) is used by [[Aristarchus of Samothrace]] as an editorial sign indicating that the line so marked is at an incorrect position. Similarly, an [[antisigma]] (encoded at U+03FD {{unicode|Ͻ}}) may mark a line that is out of place. A dotted antisigma (''antisigma periestigmenon'', encoded at U+03FF {{unicode|Ͽ}}) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority.
==Science and mathematics==
Upper case Σ is used as a symbol for:
* the [[summation]] operator
* a class of [[baryon]]s in [[particle physics]]
* macroscopic [[cross section]]s in [[nuclear physics|nuclear]] and [[particle physics]]
* in [[economics]] this letter is for the [[balance]] of the invoice classes, the overall amount of the debts and demands
* in linguistics and computer science it is used to refer to the set of symbols that form an alphabet
Lower case σ is used for:
* [[sigma bond]]s in [[chemistry]]
* the parametric [[standard deviation]] of a population (as opposed to a sample) in [[statistics]]
* a quality model for business, [[Six Sigma]], based on the [[standard deviation]], often referred to as "'''6σ'''"
* [[sigma-algebra]]s, sigma-fields and [[Sigma-finite measure|sigma-finiteness]] in [[Measure (mathematics)|measure theory]]; more generally, the symbol ''σ'' serves as a shorthand for "[[countable set|countably]]", e.g. a ''σ''-compact [[topological space]] is one that can be written as a countable [[union (set theory)|union]] of [[compact space|compact subsets]].
* the [[divisor function|sum-of-divisors function]] in [[number theory]]
* the [[Stefan-Boltzmann constant]]
* the "[[sigma factor]]" of [[RNA polymerase]]
* a measure of [[electrical conductivity]]
* [[Normal stress|Normal]] [[Stress (physics)|stress]] in [[continuum mechanics]]
* volatility of a [[stock]] generally needed for [[options pricing]]
* a [[syllable]] in [[phonology]]
* the [[spectrum of a matrix]] <math>A</math>, denoted as <math>\sigma(A)</math>, in [[applied mathematics]]
* [[surface tension]]
* In relational algebra sigma is used to define the unary operation selection on a database relation.
==Politics==
During the 1930s, an upper case Σ was in use as the symbol of the [[Brazilian Integralism|Ação Integralista Brasileira]], a radical right-wing party in [[Brazil]].
==Popular culture and use in fiction==
*In a practice similar to [[faux Cyrillic]], capital sigmas are sometimes used in place of Roman [[E]] to give a Greek flavour to titles or text.
*Author [[James Rollins]]'s books contain a fictional government agency known as Sigma Force.
* [[Mercury-Atlas 8]] was called Sigma 7.
*Sigma 2,3,5,6,7,8,9 computers produced by [[Xerox|Xerox Data Systems]] in the 1970s following purchase of SDS, Scientific Data Systems, by it. Successful range of scientific computers similar to IBM 370's.
* [http://sigmakee.sourceforge.net Sigma] is the name of a system for [[ontology]] development and reasoning
*There is a [[sorority]] named [[Sigma Sigma Sigma]] and the [[Phi Sigma Alpha]] Fraternity goes by the name of [[Phi Sigma Alpha|Sigma]] Fraternity.
*There are nine historically black Greek-letter organizations (BGLOs) that make up the National Pan-Hellenic Council. Collectively, these organizations are referred to as The Divine Nine. Members of Phi Beta Sigma are known as SIGMAs as well as members of Sigma Gamma Rho Sorority.
* Along with other Greek letters, it is used as a classification of the strength of a PSI technique.
* [[Sigma Xi]], The Scientific Research Society, was founded 1886 at [[Cornell University]] as an honor society for scientists and engineers.
* Sigma Zeta, the honor society for undergraduate science, math, and computer science founded at Shurtleff College in Alton, Illinois, in the autumn of 1925.
==See also==
*[[Antisigma]]
*[[Disigma]]
*[[Sampi]]
[[Category:Greek letters]]
[[als:Σ]]
[[ar:سيغما (حرف إغريقي)]]
[[arc:Σ]]
[[br:Sigma (lizherenn)]]
[[bg:Сигма]]
[[ca:Sigma]]
[[cs:Sigma]]
[[da:Sigma (bogstav)]]
[[de:Sigma]]
[[el:Σίγμα]]
[[es:Σ]]
[[eo:Sigmo]]
[[eu:Sigma]]
[[fr:Sigma]]
[[ga:Sigme]]
[[gd:Sigma]]
[[gl:Sigma]]
[[ko:Σ]]
[[hr:Sigma]]
[[id:Sigma]]
[[is:Sigma]]
[[it:Sigma (lettera greca)]]
[[he:סיגמא]]
[[ka:სიგმა (ასო)]]
[[ht:Σ]]
[[ku:Sigma]]
[[la:Sigma]]
[[hu:Szigma]]
[[ms:Sigma]]
[[nl:Sigma (letter)]]
[[ja:Σ]]
[[no:Sigma]]
[[nn:Sigma]]
[[nds:Sigma]]
[[pl:Sigma]]
[[pt:Σ]]
[[ru:Сигма (буква)]]
[[simple:Sigma (letter)]]
[[sk:Sigma]]
[[sl:Sigma]]
[[sh:Sigma]]
[[fi:Sigma]]
[[sv:Sigma]]
[[th:ซิกมา]]
[[tr:Σ]]
[[uk:Сигма (літера)]]
[[zh:Σ]]